1. Field of the Invention
The present invention relates generally to papermaking, and relates more specifically to multilayer fabrics employed in papermaking. The invention also relates to the binding of triple layer forming fabrics with weft yarns. The present invention also relates to multilayer papermaker's fabrics that employ weave patterns which can provide one or more of the following advantages: impart a disturbed and/or textured surface onto the paper; produce an improved three-dimensional formation of the paper sheet; produce an improved textured board or packaging paper
2. Discussion of Background Information
In the conventional fourdrinier papermaking process, a water slurry, or suspension, of cellulosic fibers (known as the paper “stock”) is fed onto the top of the upper run of an endless belt of woven wire and/or synthetic material that travels between two or more rolls. The belt, often referred to as a “forming fabric,” provides a papermaking surface on the upper surface of its upper run which operates as a filter to separate the cellulosic fibers of the paper stock from the aqueous medium, thereby forming a wet paper web. The aqueous medium drains through mesh openings of the forming fabric, known as drainage holes, by gravity or vacuum located on the lower surface of the upper run (i.e., the “machine side”) of the fabric.
After leaving the forming section, the paper web is transferred to a press section of the paper machine, where it is passed through the nips of one or more pairs of pressure rollers covered with another fabric, typically referred to as a “press felt.” Pressure from the rollers removes additional moisture from the web; the moisture removal is often enhanced by the presence of a “batt” layer of the press felt. The paper is then transferred to a dryer section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.
Typically, papermaker's fabrics are manufactured as endless belts by one of two basic weaving techniques. In the first of these techniques, fabrics are flat woven by a flat weaving process, with their ends being joined to form an endless belt by any one of a number of well-known joining methods, such as dismantling and reweaving the ends together (commonly known as splicing), or sewing on a pin-seamable flap or a special foldback on each end, then reweaving these into pin-seamable loops. A number of auto-joining machines are available, which for certain fabrics may be used to automate at least part of the joining process. In a flat woven papermaker's fabric, the warp yarns extend in the machine direction and the filling yarns extend in the cross machine direction.
In the second basic weaving technique, fabrics are woven directly in the form of a continuous belt with an endless weaving process. In the endless weaving process, the warp yarns extend in the cross machine direction and the filling yarns extend in the machine direction. Both weaving methods described hereinabove are well known in the art, and the term “endless belt” as used herein refers to belts made by either method.
Effective sheet and fiber support are important considerations in papermaking, especially for the forming section of the papermaking machine, where the wet web is initially formed. Additionally, the forming fabrics should exhibit good stability when they are run at high speeds on the papermaking machines, and preferably are highly permeable to reduce the amount of water retained in the web when it is transferred to the press section of the paper machine. In both tissue and fine paper applications (i.e., paper for use in quality printing, carbonizing, cigarettes, electrical condensers, and like) the papermaking surface comprises a very finely woven or fine wire mesh structure.
U.S. Pat. No. 5,152,326 to VOHRINGER, the disclosure of which is hereby expressly incorporated by reference in its entirety, discloses a composite papermaking fabric including an upper fabric upon which a fiber suspension will be deposited for producing paper and a lower fabric or running surface being driven by the papermaking machine. The upper and lower fabrics are connected by binding threads. Use of separate, independent binding threads or binding threads which are only a part of the upper layer is replaced by the interweaving of fabric-born threads which are an integral part of the lower fabric and fabric-born threads which are an integral part of the upper fabric. Relative slippage between the upper and lower fabric layers is eliminated or decreased and the strength of the connection is increased. The marking of the paper is decreased. The fabric-born threads of one fabric layer cross the fabric-born threads of the other after at least one length of weave pattern. VOHRINGER, however, utilizes a plain weave and vertically stacked pairs of intrinsic binders. Furthermore, the fabric of VOHRINGER is designed with a smooth surface, i.e., it utilizes a plain weave which is undisturbed and/or untextured, so as to impart this type of surface to the paper. That is, the fabric is not utilized to provide texturing to the paper. Finally, the binders in VOHRINGER are not designed to float over any crossing yarns and do not extend above a main paper side surface (as defined by an upper surface of the non-binding yarns) of the fabric and are not utilized to impart surface impressions into the paper surface, i.e., to produce a disturbed or textured surface on the paper.
U.S. Pat. No. 5,826,627 to SEABROOK et al., the disclosure of which is hereby expressly incorporated by reference in its entirety, discloses a composite forming fabric in which the woven paper and machine side layers are interconnected by pairs of intrinsic weft binder yarns which interweave with the paper side layer to occupy an unbroken weft path. Each member interweaves sequentially with the warps of the paper side layer and with at least one warp of the machine side layer. Each part of the unbroken weft path is separated from adjacent parts by at least one paper side layer warp yarn. The unbroken weft path is the same, or different, to the weft path of the immediately adjacent paper side layer weft yarns. This arrangement overcomes the paper side layer surface imperfections, which cause an unacceptable level of marking, hitherto associated with the use of additional weft binder yarns in composite fabrics. SEABROOK, however, also utilizes a plain weave and vertically stacked pairs of intrinsic weft binders. Furthermore, the fabric of SEABROOK is designed with a smooth surface, i.e., it utilizes a plain weave which is undisturbed and/or untextured, so as to impart this type of surface to the paper. That is, the fabric is not utilized to provide texturing to the paper. Finally, the weft binders in SEABROOK are not designed to float over any crossing yarns and do not extend above a main paper side surface (as defined by an upper surface of the non-binding yarns) of the fabric and are not utilized to impart surface impressions into the paper surface, i.e., to produce a disturbed or textured surface on the paper.
U.S. Pat. No. 5,967,195 to WARD, the disclosure of which is hereby expressly incorporated by reference in its entirety, discloses a multi-layer papermaker's forming fabric has stitching yarns integrated into the papermaking surface. Each of a plurality of repeating units of the fabric comprises: a set of top machine direction yarns; a set of top cross-machine direction yarns interwoven with the top machine direction yarns; a set of bottom machine direction yarns; a set of bottom cross-machine direction yarns interwoven with the bottom machine direction yarns; and pairs of first and second stitching yarns. The stitching yarn pairs are positioned between pairs of top cross-machine direction yarns. The stitching yarns of each pair are interwoven with the top and bottom machine direction yarns such that, as a fiber support portion of the first stitching yarn is interweaving with the top machine direction yarns, a binding portion of the second stitching yarn is positioned below the top machine direction yarns, and such that as a fiber support portion of the second stitching yarn is interweaving with the top machine direction yarns, a binding portion of the first stitching yarn is positioned below the top machine direction yarns. The first and second stitching yarns cross each other as they pass below a transitional top machine direction yarn. Also, each of the binding portions of the first and second stitching yarns passes below at least one of the bottom machine direction yarns. In this configuration, the stitching yarns are completely integrated into the top, or papermaking, surface of the fabric, and therefore do not adversely impact the papermaking qualities of the fabric. WARD, however, utilizes vertically stacked pairs of intrinsic weft binders. Furthermore, the fabric of WARD is apparently not designed to produce disturbed and/or textured surface onto the paper. That is, the fabric does not appear to provide texturing to the paper. Finally, the weft binders in WARD do not extend above a main paper side surface (as defined by an upper surface of the non-binding yarns) of the fabric and are not utilized to impart surface impressions into the paper surface, i.e., to produce a disturbed or textured surface on the paper.